Air filter units particularly those utilized with internal combustion engines for heavy duty trucks, and the like, normally include an outer sleeve which is formed from a blank of expanded metal or perforated sheet material which in turn, is formed into a cylindrical sleeve by a complex, time-consuming operation and/or in many instances a jagged, burr-forming edge of the blank is exposed when a seam is formed in the ultimate sleeve. Such an exposed edge is susceptible to being snagged by clothing or the like or scratching or cutting the hands or arms of the installer when the filter unit is being installed on or removed from the engine or when the components of the filter unit are being assembled.